1. Technical Field
The present invention relates to a successive approximation type analog/digital converter, a physical quantity detecting sensor, an electronic device, a moving object, and a successive approximation type analog/digital conversion method.
2. Related Art
For example, a physical quantity detecting sensor such as an acceleration sensor changes an analog signal which is a measured physical quantity to a digital signal using an analog/digital (AD) converter and outputs the digital signal. As a successive approximation type AD converter that increases the bits while keeping the small area as it is, a combination of a charge redistribution type digital/analog (DA) conversion circuit and a resistance voltage-dividing type DA conversion circuit is known. In a charge redistribution type DA converter, the capacitance is weighted in a binary ratio of “1:2:4:8:16:32.” In this manner, the conversion accuracy between the high-order bits using a charge redistribution type DA conversion circuit and the low-order bits using a resistance voltage-dividing type DA conversion circuit is degraded because of the ratio accuracy of the capacitance.
A circuit which is configured of the same unit capacitance without weighting the capacitance of a charge redistribution type DA conversion circuit and connects an output voltage of a resistance voltage-dividing type DA conversion circuit to each unit capacitance is suggested (JP-A-9-214344).
Meanwhile, a circuit in which dynamic element matching (DEM) is applied to a charge redistribution type DA conversion circuit whose capacitance is weighted in a binary ratio is suggested (JP-A-2012-175440). According to JP-A-2012-175440, since it becomes possible to provide randomness for a combination pattern of the capacitance in a capacitance array, the apparent capacitance ratio accuracy in the capacitance array can be improved.
In regard to the invention disclosed in JP-A-9-214344, improvement in the conversion accuracy between the high-order bits using a charge redistribution type DA conversion circuit and the low-order bits using a resistance voltage-dividing type DA conversion circuit is made, but the influence of the ratio accuracy of the unit capacitance in the charge redistribution type DA conversion circuit is unlikely to be improved. The main reason for the occurrence of this problem is that the unit capacitance with required ratio accuracy is hardly produced. The ratio accuracy is improved when the unit capacitance is increased, but new problems of an increase in input capacitance or an increase in circuit area are generated.
In regard to the invention disclosed in JP-A-2012-175440, a converter configured of a charge redistribution type DA conversion circuit is used. Accordingly, there is a problem in that the capacitance ratio of an AD converter becomes larger than that of the combination of a charge redistribution type DA conversion circuit and a resistance voltage-dividing type DA conversion circuit when an AD converter with the same resolution is configured and thus the circuit area is increased.